Patients suffering from a restricted or lacking renal function will have the waste products of the natural metabolism (including uremic toxins) removed by renal substitution methods or dialysis methods. Here, removing the substances from the blood, which is taken from the patient and conveyed in extracorporeal manner, is performed through the contact of the blood with a dialysis liquid; in this process, the blood and the dialysis liquid are not in direct contact, but contact each other via a semi-permeable membrane. The dialysis liquid is charged with various salts. The removal of the physiological waste products is carried out through diffusive and convective effects. These are responsible for the transport of the substances from the blood to the dialysis liquid via the membrane arranged in extracorporeal manner. Having removed a part of the waste materials, the blood which has been treated in such a manner is again returned to the patient.
For evaluating the efficiency of a dialysis session, the concentrations of uremic toxins are determined before, after and possibly also during a dialysis session. The reduction of the respective substances is the central basis for the evaluation of the dialysis dosage.
Urea is a common key metabolite which is taken for determining the dialysis dosage. Correspondingly, the urea reduction rate is said to be a crucial parameter in dialysis technology. The determination of the urea reduction can be carried out in different ways.
A classic procedure is the chemical determination of the concentration of urea in the blood, each time before and after a dialysis therapy. However, the problem of this procedure is that the blood samples have to be taken from the patient and then sent to a laboratory which is provided with an appropriate equipment for determining the concentration of urea. This process may indeed take several days. Accordingly, the determination of the dialysis dosage cannot be carried out in a timely manner and especially not during a dialysis session.